1. Field of the Invention
The present invention generally relates to a picture forming apparatus, and particularly relates to a picture forming apparatus in which a photosensitive medium is subject to exposure in accordance with picture information including character information or symbol information through a light-transmissible medium having dot information.
2. Description of the Prior Art
Conventionally, when a picture having good gradation is to be formed on a photosensitive medium such as a photo-pressure sensitive recording sheet having poor gradation, a dot screen having a light-transmissible medium having dot information is used and the photosensitive medium is exposed through the dot screen to thereby obtain a good picture having good gradation on a photosensitive medium.
FIG. 2 shows such a picture forming apparatus using a dot screen. In FIG. 2, light emitted from an exposure light source 1 for exposing a slidefilm 3 is separated into three colors, red, green and blue by a three-color separating filter 2 so that the separated light of red, green, and blue colors is successively incident upon the slidefilm 3. The light transmitted through the slidefilm 3 is condensed by a lens 4 so as to be focused on a photo-pressure sensitive sheet 7 through a dot screen 5. After completion of exposure successively with the separated light of red, green, and blue colors, a developing-sheet feeding roller 11 is driven so as to take up a developing sheet 10 from a developing-sheet cassette 9, and the developing sheet 10 and the photo-pressure sensitive sheet 7 are superposed on each other and passed through pressing rollers 13, so that the image carried by the slidefilm 3 is duplicated on the developing sheet 10. Further, the developing sheet 10 on which the picture has been formed is passed through a heat-fixing rollers 14 so as to improve the coloring and glossiness.
By the use of such an apparatus incorporating a dot screen, a picture having good gradation can be duplicated even on a photosensitive medium, such as a photo-pressure sensitive sheet or the like, having poor gradation property.
However, only a picture formed on a photosensitive medium and having soft tone and good gradation is not always preferable for a user, but there is a case where a picture having poor gradation is more preferable for the user. In this regard, it becomes necessary to remove the dot screen or to replace the dot screen by another one.
Accordingly, such a picture forming apparatus incorporating a dot screen as described above requires much labor because the exposure time or exposure light intensity must be adjusted whenever the dot screen is removed or replaced by another one.